This invention relates to electromagnetic clutches and, in particular, to clutches for use in driving refrigerant compressors for automobile air conditioning systems.
FIG. 1 illustrates a known electromagnetic clutch which is used between the engine and the compressor for selectively driving the compressor. The clutch includes a pulley 1 which is mounted on a bearing 2 mounted on a tubular bearing support or sleeve 3 of a compressor housing 4 and which is rotated by a belt shown by a dotted line from the automobile engine (not shown). Pulley 1 is provided with a plurality of concentric annular magnetic pole faces 1a at an axial end thereof. A drive shaft 5 of the compressor extends through sleeve 3. A hub 6 is fixed to the extending terminal end of drive shaft 5, and an annular armature plate 7 is joined by leaf springs 8 to hub 6 so that armature plate 7 faces the annular concentric pole faces with an axial space therebetween. An electromagnet 9 is mounted on sleeve 3, and is stationarily disposed within an annular hollow portion formed in pulley 1 to supply magnetic flux for attracting armature plate 7 to magnetic pole faces 1a.
Thus, when electromagnet 9 is energized, drive shaft 5 is rotated together with pulley 1 by the engine output, and when electromagnet 9 is not energized, pulley 1 is rotated by the engine but the compressor is not driven.
In the known electromagnetic clutch, since tubular bearing support or sleeve 3 is made integral with compressor housing 4, the wall thickness of sleeve 3 is relatively thick for the readiness of the production. In case compressor housing 4 is made of aluminum or aluminum alloy to reduce the weight of the compressor, the wall thickness of sleeve 3 is increased to obtain the mechanical strength of the sleeve sufficient to resist to the tension of the belt wound on pulley 1. Therefore, the diameter of pulley 1 is increased so that the compressor with the electromagnetic clutch becomes large, while it results in the reduction of the magnetic attraction force to reduce only the outer diameter of the pulley, so that the transmission of the rotation is degraded.
A shaft seal assembly 10 is usually disposed on drive shaft 5 within sleeve 3. Therefore, the inner diameter of sleeve 3 is required large enough to contain the shaft seal assembly in the sleeve. Accordingly, the outer diameter of the sleeve and, therefore, the diameter of the pulley are increased.
In the known arrangement shown in FIG. 1, bearing 2 is fixedly mounted on sleeve 3 by fitting the inner ring 2a on sleeve 3 and securing a retainer ring or a snap ring 11 on the outer surface of sleeve 3. Inner ring 2a is held between a shoulder portion 3a formed on sleeve portion and retainer ring 11 to be prevented from its axial movement. Although the rotation of inner ring 2a on sleeve 3 can be prevented by closely fitting inner ring 2a onto sleeve 3, the assembling operation of bearing 2 on sleeve 3 is difficult. Furthermore, once the rotation of inner ring 2a is caused on sleeve 3 for any reason, it cannot be repaired.
In another known arrangement, the sleeve is made integral with a bracket for supporting the electromagnet. Referring to FIG. 2, a bracket 12 is secured onto compressor housing 4 by screws 13, electromagnet 9 is fixedly supported by bracket 12. Bracket 12 has an integral sleeve portion 12a surrounding drive shaft 5. On sleeve portion 12a, bearing 2 is mounted which supports pulley 1.
In the arrangement, since bracket is made of steel and, therefore, the wall thickness of sleeve portion 12a can be thin, the diameter of the pulley can be reduced without degrading the transmission of the rotational force. Furthermore, in the arrangement shown in FIG. 2, since no shaft assembly is mounted within sleeve portion 12a, the outer diameter of the sleeve portion is further reduced. But, the shaft seal assembly must be assembled in the compressor housing, and this makes it difficult to repair the shaft seal assembly.
In the known arrangement shown in FIG. 2, a complex construction is employed to fixedly mount inner ring 2a of bearing 2 onto sleeve portion 12a.
Referring to FIG. 3 in addition to FIG. 2, a shoulder 12b is formed on sleeve portion 12a. Sleeve portion 12a is provided with a threaded groove 14 on the outer surface of its extended end, and with axial slits 15 in its extended end. After fitting inner ring 2a on sleeve portion 12a, a washer ring 16 is fitted on sleeve portion 12a and, thereafter, a nut 17 is threaded on extended end of sleeve portion 12a. Inner ring 2a is pushed to shoulder 12b by tightening nut 17 and is tightly held between shoulder 12b and washer ring 16, so that it is prevented from not only its axial movement but also rotation. In order to prevent nut 17 from loosing, washer ring 16 is provided with radially inwardly projecting projections 16a which are fitted in axial slits 15 to prevent the rotation of washer ring 16. Washer ring 16 is also provided with a plurality of radial outer projections 16b, while nut 17 is provided with a plurality of axial grooves 17 a on its outer surface. After tightening nut 17, outer projections 16b are bent to engage with axial grooves 17a, so that nut 17 is prevented from loosing.
The arrangement is complex but is not so sufficient to prevent the inner ring of the bearing from rotating because the preventing force is merely due to the contact force of the inner ring with the washer ring and the shoulder.